The application of an orthopedic cast to an extremity requires that the extremity be positioned or immobilized in a certain attitude. The attitude is chose to achieve optimal alignment of a joint or optimal degree of inclination of a bone to ensure that the broken parts of a bone are kept in apposition during the procedure.
A fibular or tibial fracture, for example, may require that the lower leg bones not incline from the horizontal during cast application, whereas a dislocation at the knee joint may require the lower leg bones to be positioned so as to form a knee joint angle other than ninety degrees while the cast is applied.
Injuries to the ankle may call for flexion or extension of the joint, and in some instances for inversion or eversion, while the injured joint is wrapped.
Similarly, a fracture of the lower arm bones may necessitate pronation or supernation of the forearm to put the fractured parts in apposition before a cast is applied.